Electron discharge devices



April 22, 19158 .J M. STINCHFIELD 2,832,050

' ELECTRON DISCHARGE DEVICES Filed March 22, 1945 INVENTOIS.filmfiqaagll wfiaw flrro/zwiy UnitedStates Patent 2,832,059 ELECTRONDISCHARGE DEVICES John Maxwell Stiuchfield, Monmouth Junction, N. J.,as-

signor to Radio Corporation of America, a corporation of DelawareApplication March 22, 1945, Serial No. 584,136 Claims. (Cl. 332-5) Myinvention relates to ultra high frequency apparatus such as electrondischarge devices employing cavity resonators and more particularly tomagnet-tons employing cavity resonators and to means for tuning andmodulating the same.

Magnetrons employing cavity resonators usually include a cathodesurrounded by a plurality of anode segments, the cavity resonators beingcoupled between adjacent. segments. The anode assembly may be made froma solid block of conducting material with a central chamher having slotsradiating therefrom, which may or may not be enlarged at their outerends, to provide cavity resonators, the portions of the block 1 etweenthe slots providing the anode segments. In another type of constructiona conductor ring supports a plurality of radially directed vanes orslats, the inner ends providing the anode segments and defining acentral chamber in which the cathode is placed.

Various attempts have been made to tune this type of apparatus and tomodulate the same. This usually required moving parts within theenvelope of the magnetron or within the cavity resonators, complicatingthe structure and introducing undesirable modes of operation. Acontinuous tuning range with a uniform distribution of intensities inthe standing wave pattern and in the desired mode of oscillation wouldnot always result.

It is, therefore, an object of my invention to provide an electrondischarge device of the magnetron type employing cavity resonators ofimproved design which can be tuned and modulated.

Another object of my invention is to provide such a device which can betuned over a large continuous tuning range with a uniform distributionof intensities in a standing wave pattern and in the desired mode ofoscillation.

A still'further object of-my invention is to provide a device of thehind described, which can be tuned or modulated by means external to thedevice.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFigure 1 shows a side elevation of an electron discharge device madeaccording to my invention, Figure 2 is a transverse section taken alongthe line 2-2 of Figure 1, Figure 3 shows a modification of a detail ofthe apparatus shown in Figures 1 and 2 and Figure 4 is an axial sectionof a modified electron discharge device embodying my invention.

In the embodiment 'of my invention shown in Figure 1 an anode block 19of conducting material has provided at its axis a central cylindricalchamber 11, at the axis of which is mounted an indirectly heated-cathode12 provided with heater and cathode leads l3 and 1d extend ing throughtubular members 15 and 16 and sealed vacuum-tight by means of insulatingcup-shaped members 17 and 18.

The attode block is provided with a pluralityot radially directed slots19 communicating with enlarged cylinder like chambers 29, thelongitudinal axes of which extend parallel to the cathode. The slots 19and chambers 26 provide cavity resonators connected between adjacentanode segments 19 formed by slots 19. The output may be taken by theusual loop 21, the extension of which forms the inner conductor 21?. ofa coaxial line, the outer conductor 22 of which is sealed vacuum-tightat 23 and has a screw portion 24 which may cooperate with an extension(not shown) of the outer tubular member 22 to extend the coaxial line orto couple the device to radiator. Magnets 43 and 44 provide the usualmagnetic field parallel to the cathode in the cathode-anode space.

In a preferred embodiment of my invention I strap alternate anodesegments together by means of conducting straps such as 25 and 26 toinsure the desired vr -mode of operation whereladjacent segments operate180 out of phase with each other. The other intermediate segments may beconnected by straps 25 and 26 on the other side of the anode block.

In order to tune the device over a wide range, I employ a tunableresonator coupled in a manner to be described to the strap 26 within theenvelope of the device. The tunable resonator illustrated is of thecoaxial line type, and includes an outer conductor 30 and innerconductor 31, the ends being closed by a conducting disc 32. The innerconductor 31 is connected to inner conductor 33, which is electricallyconnected to the strap 26 at a point intermediate its connection withthe anode segments 19. The outer conductor 3d is connected to acone-shaped element 34 having a tubular extension 35 of reduced diameterreceived Within a bore 36 in the block 10 and a channel 36 in the anodesurface and terminating close to the strap 26. Thus, the coaxial linetuning resonator is connected to each pair of adjacent anode segments. Avacuum-tight seal 34 is provided between the inner conductor 33 and themember 34. The coaxial line resonator may be tuned by the slidableshorting ring 38 operated by means of the handle 39.

This arrangement insures a large continuous tuning range with a uniformdistribution of intensities in a standing wave pattern and in thedesired mode of oscillation. Best results are obtained when the coaxialtuning resonator is completely enclosed, as shown, up to the point ofconnection with the cavity resonator circuits. At the point ofconnection between the coaxial tuning resonator and the cavities, thetwo circuits are joined so that the leakage reactance between them is asnear zero as possible. The inner conductor is joined to the heavystrapping conductor 26 joined to the highest potential points of likepolarity on the alternate vanes or anode segments. These heavy straps,preferably of cop per, permit the flow of large tuning currents. Theouter conductor of the coaxial resonator may be made a part of the solidsegment between two cavities as shown in Figure 1 or a part of the vanesif these are employed in the manner shown in. my copending application,Serial No. 584,137 filed March 22, 1945, now Patent No. 2,591,976, datedApril 8, 1952, assigned to the same assignee as the present application.It is desirable to have the size and the position of the coaxialresonators such that no extraneous modes of oscillation are introduced,that is the electrical symmetry of the cavities should not be toogreatly altered.

The point of connection of the tuning resonator to the cavity is locatedso that a strong resonance occurs in the desired mode of oscillation andno other strong resonance occurs in the operating range of frequencies.The desired mode of oscillation is the so-called 1r-mode, in which theanode segments are alternately positive and negative at a given instant.Usually this condition is obtained when there is just enoughnon-symmetry between the angular position of the tuning resonator andthat of I, the output line to avoid setting up other modes of oscillation. For example, the position of the tuning resonator with respectto the load line is less than 90. If an exact 90 symmetry occurs thenother disturbing modes of oscillation may also appear. In order toobtain a wide tuning range it is necessary to choose inductance,capacitance and loss characteristics of the tuning resonator withrespect to the equivalent characteristics for the loaded cavityresonators.

The tuning resonator may be connected externally to any one of a numberof tunable circuit arrangements. For example, as shown a shortcircuiting ring may be used to change the eflfective length of theresonator. Or an open-ended resonator could also be utilized where thelength of the center conductor is varied to tune the tube. Such anarrangement is shown in Figure 3. Here a conductor within which ismounted an inner conductor 31, having telescoped thereover a tubularmember 31" fastened to an insulating rod 39'. The effective length ofinner member 31 is varied by moving a tubular member 31". A tunablecavity resonator may also be coupled to the open-ended resonator. Asmall variable capacitance in conjunction with the open-ended resonatorwill also tune the tube. Thus tuning of the tuning resonator is notlimited to the form shown.

The same principle may be employed for frequency modulating themagnetron. This may be accomplished by the addition of a second coaxialline resonator 40, 41 as shown connected to a modulating circuit 42 inFig. 2. The inner conductor is sealed vacuum-tight to the outerconductor 41 by means of the insulating seal 40'. By means of thiscircuit the reactance of the resonator is changed which in turn effectsthe frequency of the cavity resonators within the tube at the modulatingfrequency. While for purposes of illustration the coaxial line resonator40, 41 is shown connected to strap 25, for best results it would beconnected to another strap such as 26' on the other side of the tube andin a position other than 90 to the output line. Thus not only may theresonant frequency of the device be changed from one frequency toanother by means of a tuned coaxial line resonator, but the device mayalso be frequency modulated at these different resonant frequencies.

Figure 4 illustrates my invention embodied in a vanetype magnetron asshown in my above-mentioned copending application. This magnetroncomprises a drumshaped metallic envelope containing a plurality ofradially-extending fiat, metallic, anode vanes 51. The inner edges ofthe vanes 51 provide anode segments and define a cylindrical cathodespace 52 in which a cathode 53 is axially mounted. Each pair of adjacentvanes together with the portion of the envelope therebetween constitutesa cavity resonator. A metallic strapping ring 54 is connected to onegroup of alternate anode vanes near the inner edges thereof. Theremaining alternate vanes are connected together by a second metallicstrapping ring 55 which may be arranged concentric with the ring 54, asshown.

In order to tune the magnetron a tuning resonator 56, preferably of thecoaxial line type, is connected to the vane structure in a mannersomewhat similar to that shown in Figures 1 to 3. The inner conductor 57of resonator 56 is connected to the inner strapping ring 54. The outerconductor 58 of the tuning resonator extends radially inwardly along andin contact with one of the vanes 51 and is connected directly to theouter strapping ring 55. The tuning resonator 56 may be tuned by meansof a slidable shorting ring, or by other means. The operation of thetuning resonator in varying the resonant frequency of the system issimilar to that described above for Figures 1 to 3.'

While I have indicated the preferred embodiments of my invention ofwhich I am now'aware and have also indicated only one sp cificapplication for'whichfmy invention may be employed, it will be apparentthat my invention is by no means limited to the exact forms illustratedor the use indicated, but that many variations may be made in theparticular structure used and the purpose for which it is employedwithout departing from the scope of my invention as set forth in theappended claims.

What I claim as new is:

1. An electron discharge device including an anode block having acentral cylindrical chamber and a plurality of radially directed slotscommunicating with said chamber, anode segments between said slots, anda cathode adjacent said anode block for supplying elec trons within saidcentral cylindrical chamber, a conducting strap connecting alternateanode segments,and means for varying the frequency of said electrondischarge device and including a tunable coaxial line resonator, theinner conductor of which is connected to an intermediate point on saidstrap and the outer conductor of which is connected to the segmentintermediate the segments connected by said strap.

2. An electron discharge device including an anode block having acentral cylindrical chamber and a plurality of radially directed slotscommunicating with said chamber, said slots being enlarged at theirouter ends, whereby anode segments connected by cavity resonators areprovided, and a cathode adjacent said anode block for supplyingelectrons within said central chamber, a conducting strap connectingalternate anode segments, means for tuning said electron dischargedevice and including a coaxial line resonator, the inner conductor ofwhich is connected to an intermediate point on said strap and the outerconductor of which is connected to a segment intermediate the segmentsconnected by said strap. and an adjustable tuning ring within saidcoaxial line resonator for tuning said coaxial line resonator.

3. An electron discharge device including an anode block having a.central cylindrical chamber and a plurality of radially directed slotscommunicating with said chamber, anode segments between said slots, anda cathode adjacent said anode block for supplying electrons within saidcentral cylindrical chamber, a conducting strap connecting alternateanode segments, and means for varying the frequency of said electrondischarge device and including a tunable coaxial line resonator, saidanode block having a bore extending radially from the outside of saidblock toward the wall of an anode segment, the inner ends of saidcoaxial line resonator being received within said bore, the innerconductor being connected to an intermediate point on said strap, andthe outer conductor contacting said anode block.

4. An electron discharge device including an anode block having acentral cylindrical chamber and a plurality of radially directed slotscommunicating with said chamber, said slots defining anode segments, anda cathode adjacent said anode block for supplying electrons within saidcentral chamber, a conducting strap connecting alternate anode segments,and means for varying the frequency of said electron discharge deviceand including a tunable coaxial line resonator having an outer tubularmember having a reduced inner end and a closed outer end, and an innerconductor, said anode block having a bore extending from the exteriorthereof toward the wall of the anode segment intermediate the segmentsconnected by said strap, the inner end of said coaxial line resonatorextending within said bore, the inner conductor being connected to saidstrap and the outer tubular conductor to the walls of said bore, and atuning member within said coaxial line resonator, the inner conductor ofwhich is connected to an intermediate point on said strap and the outerconductor of which is connected to the intermediate segments connectedby said strap.

5. An electron discharge device of the magnetron type having anelectrode assembly including a cathode and a plurality of anode segmentsadjacent said cathode, cavity resonators connecting adjacent anodesegments, a conducting strap connecting a pair of alternate anodesegments, means for tuning said electron discharge device and includinga coaxial line resonator having one conductor connected to said strapintermediate the ends of said strap and another conductor connected tothe anode segment intermediate the anode segments connected by saidstrap, a second strap connected to another pair of alternate anodesegments, and means for frequency modulating said electron dischargedevice including a second coaxial line resonator having one conductorconnected to said second strap and the other conductor connected to theanode segment intermediate the segments connected to said second strap.

6. An electron discharge device of the magnetron type having anelectrode assembly including a cathode and a plurality of anode segmentsadjacent said cathode, cavity resonators connecting adjacent anodesegments, a con ducting strap connecting a pair of alternate anodesegments, means for tuning said electron discharge device and includinga coaxial line resonator having an inner conductor connected to saidstrap intermediate the ends of said strap and its outer conductorconnected to the anode segment intermediate the anode segments connectedby said strap, a second strap connected to other alternate anodesegments, and means for frequency modulating said electron dischargedevice including a second coaxial line resonator having its innerconductor connected to said second strap and the outer conductorconnected to an anode segment intermediate the segments connected tosaid second strap.

7. An electron discharge device of the magnetron type including an anodeblock having a central cylindrical chamber and a plurality of radiallydirected slots communicating with said chamber, said slots providinganode segments therebetween, and a cathode adjacent said anode block forsupplying electrons within said central cylindrical chamber, aconducting strap connecting a pair of alternate anode segments, meansfor tuning said electron discharge device and including a tunablecoaxial line resonator, the inner conductor of which is connected to anintermediate point on said strap and the outer conductor of which isconnected to the segment intermediate the segments connected by saidstrap, a second strap connected to another pair of alternate anodesegments, and means for frequency modulating said electron dischargedevice including a second coaxial line resonator having its innerconductor coupled to said second strap and its outer conductor to theanode segment intermediate the segments connected by said second strap.

8. An electron discharge device of the magnetron type having anelectrode assembly including a cathode and a plurality of anode segmentsadjacent said cathode, cavity resonators connected between adjacentanode segments, a

conducting strap connecting alternate anode segments, means for varyingthe frequency of said electron discharge device and including a coaxialline resonator having inner and outer conductors, one of said conductorsbeing connected to said strap and the other of said conductors to theanode segment intermediate the anode seg ments connected by said strap,and means connected to said coaxial line resonator for applying amodulating voltage between said inner and outer conductors.

9. An electron discharge device of the magnetron type having anelectrode assembly including a cathode and a plurality of anode segmentsadjacent said cathode, cavity resonators connected between adjacentanode segments, a conducting strap connecting alternate anode segments,means for varying the frequency of said. electron discharge device andincluding a coaxial line resonator having inner and outer conductors,one of said conductors being connected to said strap and the other ofsaid conductors to the anode segment intermediate the anode segmentsconnected by said strap, means connected to said coaxial line resonatorfor applying a modulating voltage between said inner and outerconductors, and means within said coaxial line resonator for tuning saidresonator to vary the resonant frequency of said electron dischargedevice.

10. An electron discharge device of the magnetron type having anelectrode assembly comprising a cathode for supplying electrons and aplurality of anode segments adjacent said cathode for receiving saidelectrons, cavity resonators connected between adjacent anode segmentsand normally operable at a predetermined resonant frequency, and meansfor varying the frequency of said electron discharge device andincluding a tuning resonator having two conductors respectivelyconnected to two adjacent anode segments and means connected to saidtuning resonator for applying a modulating voltage between said twoconductors.

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